Updated with additional information from the press conference, copy of the case.

Eight same-sex couples in Missouri have filed suit seeking to have their out-of-state marriages recognized in the state.

The American Civil Liberties Union filed the suit in Kansas City this morning. The plaintiffs are not looking to force Missouri to issue marriage licenses to same-sex couples. Rather, they are challenging the state constitutional amendment defining marriage as between a man and a woman on the grounds that it denies the benefits of marriage solely on the basis of sex and sexual orientation.

Governor Jay Nixon announced in November that same-sex couples living in the state who were legally married elsewhere would be eligible to jointly file their state tax returns. But, said ACLU legal director Tony Rothert, the benefits of marriage extend beyond taxes, including:

Having a spouse’s name on a death certificate

Access to state retirement plans and survivor benefits

Visits to a nursing home or a hospital room

The right to make medical decisions if a spouse becomes incapacitated

Not being forced to testify against a spouse in a criminal trial

Ongoing coverage on dental, medical or vision insurance plans after a spouse dies

Applying for a drunk driving victim memorial sign

Though the court case alleges a federal civil rights violation, Rothert says it was a conscious decision to file a challenge to the state constitution in state court.

"We believe that the people of Missouri, when they passed the amendment, didn’t intend the harm to these families that this amendment causes," Rothert said. "We think that this is an issue that Missouri judges and the state of the Missouri should handle itself without federal judges intervening."

Sixteen states and the District of Columbia currently issue marriage licenses to same-sex couples.

That number will go up to 17 on June 1, when Illinois’ marriage equality law takes effect. All of those states recognize same-sex marriages performed outside their borders.

Shortly after the ACLU officially announced the filing, a federal judge in Kentucky struck down that state’s ban on recognizing out-of-state same-sex marriages. Ohio was also ordered by a court to do so. Wyoming recognizes same-sex marriages for the purpose of allowing divorce.

Real world implications

Alan Ziegler and LeRoy Fitzwater, two of the plaintiffs, got married in California in 2008. That marriage allowed Ziegler to accompany Fitzwater right up to the door of the operating room when Fitzwater needed an emergency appendectomy – much to the relief of Fitzwater’s parents, who were 3,000 miles away.

It was scary, Ziegler said, to lose that protection when the couple moved to St. Louis last year.

"Not only are the protections from our marriage important to us, they are important to our families as well," Ziegler said. "It gave LeRoy’s parents peace of mind being so far away that our marriage was respected."

In 2011, Zuleyma Tang-Martinez, a biology professor at the University of Missouri-St. Louis, tried twice to add her wife Arlene Zarembka to her health insurance through the University of Missouri system. The couple married in Canada in 2005.

“The university benefits officer wrote, ‘Because the University of Missouri follows Missouri state law’s definition of a lawful marriage, Arlene Zarembka is not eligible for dependent coverage.'" Tang-Martinez said.

In announcing that he would require the Department of Revenue to accept joint returns from same-sex couples, Governor Nixon, a Democrat, said he was required to do so because the U.S. treasury department had decided to recognize the marriages of same-sex couples even if they were living in states that banned such marriages. What's more, state law requires those filing jointly at the federal level to also file jointly at the state level.

Democratic Attorney General Chris Koster backed Nixon's reasoning in a statement, saying the governor appeared to be following state law on tax filing.

"The Attorney General's role is to defend such state laws to the extent possible, and not to presume that our legislature's actions violate our state's constitution,” Koster’s statement said. Koster is former Republican who split from his party on social issues, and is running for governor in 2016 as a Democrat.

State Rep. Chuck Gatschenberger, a conservative Republican from St. Charles County, demanded an official legal opinion from Koster's office on the constitutionality of the executive order.

"The voters of Missouri overwhelmingly passed an amendment to our state Constitution defining marriage as between a man and a woman,” Gatschenberger said at the time. “The governor is sworn to uphold Missouri’s Constitution."

In an opinion dated Dec. 2, 2013, deputy attorney general Joe Dandurand repeated Koster's assertion that Nixon's move was authorized by state law. But he declined to address its constitutionality, saying, "It is the longstanding policy of the Attorney General's Office-during the administrations of attorneys general from both political parties-not to opine as to the constitutionality of statutes."